(a) Field of the Invention
The present invention relates to a system for selecting a switched beam by using a plurality of antennas, and a method thereof. More specifically, the present invention relates a system for efficiently selecting a switched beam with a lesser error rate by performing less calculation, and a method thereof.
(b) Description of the Related Art
FIG. 1 shows a schematic diagram for representing an operation of a switched beam.
A switched beamforming method is one of smart antenna methods, in which a directional beam is provided toward a mobile terminal since a plurality of antennas respectively have different weight values so as to provide maximized received power to the mobile terminal.
A base station 100 includes a plurality of antenna elements 101, 102, and 103 for each sector. A mobile subscriber station 200 transmits and receives traffic data to/from the base station while moving around in a sector.
As described above, when the different weight values are respectively provided to the antenna elements 101, 102, and 103 of the base station to provide an optimized received power to the subscriber station, a beam radiated by the antenna is formed in a direction of the subscriber station.
Here, a weight value vector for the antenna element according to a beamforming direction is defined by a predetermined number, and is selected for forming a beam in an appropriate direction.
Therefore, since a directional beam that is narrower than a sector antenna is used when the above switched beamforming method is used, a beamforming gain and co-channel interference may be reduced, and system performance may be improved.
In addition, in the switched beamforming method according to the prior art, the base station arranges beamforming weight value vectors, and uses an uplink signal transmitted from the subscriber station to estimate a direction of arrival (DOA) of the uplink signal to the base station.
The base station uses the estimated DOA to determine an appropriate switched beam for the subscriber station, and transmits user traffic data by using the switched beam.
However, in the conventional switched beamforming method, sequential uplink signals of a predetermined subscriber station must be used to sequentially estimate the DOA of the signals transmitted by the predetermined subscriber station. Accordingly, resources are wasted since it is required to continuously provide the uplink signals to estimate the DOA. In addition, it is required to define an additional process to allocate uplink resources to the subscriber station so that the base station may estimate the DOA.
Furthermore, since the base station selects the switched beam for the beamforming direction, a load is increased at the base station, and a considerable length of uplink signal is used for each terminal to estimate the DOA. In addition, since an uplink frequency band and a downlink frequency band are apart from each other in frequency division duplex (FDD) method, an error occurs due to a frequency difference when the DOA estimated by using the uplink signal is used to select a downlink switched beam.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.